Preparation of multimodal polymer compositions using multinuclear metallocene catalysts

ABSTRACT

A process is provided for preparing polymer compositions which are multimodal in nature. The process involves contacting, under polymerization conditions, a selected addition polymerizable monomer with a metallocene catalyst having two or more distinct and chemically different active sites, and a catalyst activator.

TECHNICAL FIELD

This invention relates generally to the field of catalyticpolymerization processes, and more particularly relates to a catalyticmethod for preparing multimodal polymer compositions.

BACKGROUND

Polymer compositions which are referred to as "multimodal" are typicallymultimodal with respect to molecular weight, i.e., the compositionscontain two or more molecular weight distributions as may be determined,for example, by the appearance of two or more peaks in a gel permeationchromatogram or the like. However, the term "multimodality" can alsorefer to other characteristics of a polymer composition as well, e.g.,compositional distribution (the distribution of comonomers within acopolymer), tacticity distribution (wherein a polymer compositioncontains at least two segments of differing tacticity, long-chainbranching distribution, and the like. Polymeric compositions that aremultimodal are frequently more useful than compositions that are not;for example, multimodal polymer compositions can have improvedTheological behavior, higher mechanical strength and increasedelasticity relative to corresponding compositions which are notmultimodal.

Several processes are known for preparing multimodal polymercompositions. As discussed in U.S. Pat. No. 5,032,562 to Lo et al., oneprocess involves the use of tandem reactors operated in series, so thatin a first reactor an olefinic monomer is catalytically polymerized inthe presence of hydrogen, with the product then transferred to a secondreactor wherein polymerization is conducted in the presence ofrelatively large amounts of hydrogen. In this way, the higher molecularweight polymer is produced in the first reactor, and the lower molecularweight polymer is produced in the second reactor.

U.S. Pat. No. 5,525,678 to Mink et al. provides a supported catalystcomposition for producing a polyolefin resin having a high molecularweight component and a low molecular weight component, wherein thecatalyst composition contains a first catalyst which is a metalloceneand a second catalyst which is a non-metallocene. The ratio of the highmolecular weight and low molecular weight components in the polymericproduct is determined by the ratio of the concentration of the twometals in the two-component catalyst composition. In addition, U.S. Pat.No. 4,659,685 to Coleman, III et al. pertains to a two-componentcatalyst composition for preparing polyolefins having a molecular weightdistribution which is multimodal, the catalyst composition comprising amixture of a supported titanium compound and a separately supported ornon-supported organometallic compound.

U.S. Pat. No. 5,032,562 to Lo et al., cited above, also relates to asupported olefin polymerization catalyst composition for producing highdensity polyethylene ("HDPE") having a multimodal molecular weightdistribution. The catalyst composition comprises: (1) a catalystprecursor supported on a porous carrier, and (2) a catalyst activator inthe form of a mixture of conventional Ziegler-Natta cocatalysts.Katayama et al., "The Effect of Aluminium Compounds in theCopolymerization of Ethylene/α-Olefins," in Macromol. Symp. 97:109-118(1995), provides a similar system for preparing a polymer compositionhaving a bimodal composition using a two-component catalyst comprised ofa metallocene (Cp₂ ZrCl₂) and either [Ph₃ C⁺ ][B(C₆ F₅)₄ ₋ ] or [PhMe₂NH⁺ ][B(C₆ F₅)₄ ⁻ ].

In addition, certain types of metallocene catalysts have been used toproduce polymers having a specific bimodal or multimodal molecularweight distribution.

PCT Publication No. WO92/00333, inventors Canich et al., and EP 416,815A2, inventors Stevens et al., are also of interest insofar as thereferences describe metallocene catalysts for preparing polyolefins.Canich et al. describes metallocene catalyst compositions for producinghigh molecular weight polyolefins having a relatively narrow molecularweight distribution, wherein the catalyst composition is comprised of(1) a metallocene containing a Group IVB transition metal coordinated toa cyclopentadienyl ligand, and (2) a coordination complex such as ananionic complex containing a plurality of boron atoms, which serves as acatalyst activator. The metallocene catalysts described may bemononuclear or binuclear (i.e., containing one or two metal atoms whichserve as the active sites); the binuclear compounds dissociate duringpolymerization. Stevens et al. also pertains to metallocene catalysts toprepare addition polymers, particularly homopolymers and copolymers ofolefins, diolefins, "hindered" aliphatic vinyl monomers and vinylidenearomatic monomers. The Stevens et al. catalysts are metal coordinationcomplexes having constrained geometry, and are used in conjunction witha cocatalyst compound to form a complete catalytic system. Theconstrained geometry of the catalysts is stated to be of key importanceinsofar as the metal atom in the metallocene presumably is a more"exposed" active site.

Thus, the art provides metallocene catalyst compositions for producingpolymers, particular polyolefins, which have a multimodal molecularweight distribution. However, such prior catalysts and catalystcompositions either require two or more components, e.g., two catalystsused in combination, or involve binuclear compounds which break apartinto two separate components during the polymerization process (as inthe bimetallic catalyst disclosed by Canich et al.), giving rise topotential manufacturing problems, e.g., phase separation or the like,and/or loss of control over the molecular weight distribution of thepolymer composition prepared. In addition, the known metallocenecatalysts can be relatively difficult and time-consuming to synthesize,requiring expensive equipment, extreme reaction conditions, andmulti-step processes which ultimately result in a low yield of thedesired product.

Accordingly, there is a need in the art for a simpler way ofcatalytically preparing multimodal polymer compositions. Preferably,such a process would involve a single catalyst which does not requirethe presence of a second catalyst, which retains its structure duringthe polymerization process, and is relatively simple to synthesize. Thepresent invention is directed to such a process, and is based on the useof such catalysts to prepare multimodal polymers, particularlypolyolefins. The novel process calls for multinuclear metallocenecatalysts having two or more distinct and chemically different activesites. Use of such catalysts allow for a high degree of control over themultimodality of the final polymer composition, and provide for all ofthe advantages typically associated with metallocene catalysts, i.e.,versatility and use in conjunction with a variety of monomer types, theability to control the degree of vinyl unsaturation in the polymericproduct, the capability of providing isotactic or syndiotactic polymers,and the like. The polymerization process may, if desired, be carried outusing supported catalysts.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the invention to provide a methodfor preparing a multimodal polymer composition.

It is another object of the invention to provide such a method whereinthe polymer composition has a multimodal molecular weight distribution.

It is still another object of the invention to provide such a processwhich is conducted catalytically.

It is yet another object of the invention to provide such a processwhich employs a single metallocene catalyst.

It is a further object of the invention to provide such a process whichemploys a metallocene catalyst having two or more distinct andchemically different active sites.

It is still a further object of the invention to provide such a processin which the multimodal polymer prepared comprises a polymer derivingfrom the polymerization of addition polymerizable monomers containingone or more degrees of unsaturation.

It is yet a further object of the invention to provide such a process inwhich the multimodal polymer prepared is a polyolefin such aspolyethylene.

It is still a further object of the invention to provide multimodalpolymer compositions prepared by the processes disclosed herein.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing, or may be learned by practice of the invention.

The polymerization process herein involves the use of metallocenecatalysts having two or more distinct and chemically different activesites. Preferred catalysts are described in co-pending, commonlyassigned U.S. patent application Ser. No. 08/951,949, now U.S. Pat. No.5,892,079 entitled "NOVEL METALLOCENE CATALYSTS AND ASSOCIATED METHODSOF PREPARATION AND USE," filed on even date herewith. Briefly, suchpreferred catalyst compounds have the structure B(Z)_(q) as shown inFormula (I) ##STR1## wherein: B is a covalent bridging group comprisinga C₁ -C₂₄ hydrocarbyl radical optionally containing a Group IVB element,a Group VB element, or both a Group IVB element and a Group VB element,and is capable of binding up to n_(max) substituents through singlecovalent bonds;

R and R¹ are independently selected from the group consisting ofhalogen, C₁ -C₂₄ hydrocarbyl, C₁ -C₂₄ hydrocarbyl substituted with oneor more halogen atoms, and C₁ -C₂₄ hydrocarbyl-substituted Group IVBelements, x is 0, 1, 2, 3 or 4, and y is 0, 1, 2, 3 or 4, with theproviso that the sum of x and y cannot exceed 4, or, when R and R¹ areortho to each other and x and y are each 1 or greater, R and R¹ they cantogether form a five- or six-membered cyclic structure optionallysubstituted with one to four substituents selected from the groupconsisting of halogen, C₁ -C₂₄ hydrocarbyl, C₁ -C₂₄ hydrocarbylsubstituted with one or more halogen atoms, and C₁ -C₂₄hydrocarbyl-substituted Group IVB elements;

Q is cyclopentadienyl, indenyl, fluorenyl, indolyl or aminoboratobenzyl,optionally substituted with one or more R and R¹ substituents as above,or Q is J(R²) _(z-2) wherein J is an element with a coordination numberof three from Group VB or an element with a coordination number of twofrom Group VIB, R² is selected from the group consisting of hydrogen, C₁-C₂₄ hydrocarbyl, C₁ -C₂₄ hydrocarbyl substituted with one or morehalogen atoms, and C₁ -C₂₄ alkoxy, and z is the coordination number ofJ, and further wherein Q substituents on different Z groups may belinked through a C₁ -C₂₄ hydrocarbylene bridge;

M is a Group IIIA element, a Group IVA element, a Group VA element, alanthanide, or an actinide;

X is selected from the group consisting of hydride, halide, alkoxy,amido, C₁ -C₂₄ hydrocarbyl, C₁ -C₂₄ hydrocarbyl radicals substitutedwith one or more electron-withdrawing groups, and C₁ -C₂₄hydrocarbyl-substituted Group IVB elements, or, when two or more Xsubstituents are present, they may together form an alkylidene olefin,acetylene, or a five- or six-membered cyclic hydrocarbyl group;

Y is a neutral Lewis base;

m is 1, 2, 3 or 4, and n is 0, 1, 2 or 3, with the proviso that if M isa group IIIA element m is 1 and n is 0, and with the further provisothat if M is a Group IVA element, the sum of m and n does not exceed 2;

q is an integer in the range of 2 to q_(max), wherein q_(max) is equalto 1/2n_(max) when n_(max) is an even number, and 1/2(n_(max) -1) whenn_(max) is an odd number; and

the Z substituents bound to B are structurally different.

The polymerization process may involve the use of a catalytic support.Conventional inert inorganic support materials are used, e.g., oxides ofsilicon, aluminum or the like. Typically, polymerization involvescontacting selected monomers with the metallocene catalyst underreaction conditions effective to provide the desired polymercomposition. Polymerization may be carried out in solution, in a slurry,or in the gas phase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a gel permeation chromatogram for a polymer compositionprepared at room temperature using a binuclear metallocene catalyst ofthe invention.

FIG. 2 is a gel permeation chromatogram for a polymer compositionprepared using the same catalyst and a polymerization temperature of 70°C.

DETAILED DESCRIPTION OF THE INVENTION

Definitions and Nomenclature:

Before the present compounds, compositions and methods are disclosed anddescribed, it is to be understood that this invention is not limited tospecific molecular structures, ligands, or the like, as such may vary.It is also to be understood that the terminology used herein is for thepurpose of describing particular embodiments only and is not intended tobe limiting.

It must be noted that, as used in the specification and the appendedclaims, the singular forms "a," "an" and "the" include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to "an electron-withdrawing group" as in a moiety "substitutedwith an electron-withdrawing group" includes more than oneelectron-withdrawing group, such that the moiety may be substituted withtwo or more such groups. Similarly, reference to "a halogen atom" as ina moiety "substituted with a halogen atom" includes more than onehalogen atom, such that the moiety may be substituted with two or morehalogen atoms, reference to "a substituent" includes one or moresubstituents, reference to "a ligand" includes one or more ligands,reference to "a monomer" includes mixtures of different monomers, andthe like.

The term "alkyl" as used herein refers to a branched or unbranchedsaturated hydrocarbon group of 1 to 24 carbon atoms, such as methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, octyl, decyl,tetradecyl, hexadecyl, eicosyl, tetracosyl and the like, as well ascycloalkyl groups such as cyclopentyl, cyclohexyl and the like. The term"lower alkyl" intends an alkyl group of 1 to 6 carbon atoms, preferably1 to 4 carbon atoms.

The term "alkylene" as used herein refers to a difunctional saturatedbranched or unbranched hydrocarbon chain containing from 1 to 24 carbonatoms, and includes, for example, methylene (--CH₂ --), ethylene (--CH₂--CH₂ --), propylene (--CH₂ --CH₂ --CH₂ --), 2-methyl-propylene (--CH₂--CH(CH₃)--CH₂ --), hexylene (--(CH₂)₆ --), and the like. "Loweralkylene" refers to an alkylene group of 1 to 6, more preferably 1 to 4,carbon atoms.

The term "alkenyl" as used herein refers to a branched or unbranchedhydrocarbon group of 2 to 24 carbon atoms containing at least onecarbon-carbon double bond, such as ethenyl, n-propenyl, isopropenyl,n-butenyl, isobutenyl, t-butenyl, octenyl, decenyl, tetradecenyl,hexadecenyl, eicosenyl, tetracosenyl and the like. Preferred alkenylgroups herein contain 2 to 12 carbon atoms and 2 to 3 carbon-carbondouble bonds. The term "lower alkenyl" intends an alkenyl group of 2 to6 carbon atoms, preferably 2 to 4 carbon atoms, containing one--C═C--bond. The term "cycloalkenyl" intends a cyclic alkenyl group of 3 to 8,preferably 5 or 6, carbon atoms.

The term "alkenylene" refers to a difunctional branched or unbranchedhydrocarbon chain containing from 2 to 24 carbon atoms and at least onecarbon-carbon double bond. "Lower alkenylene" refers to an alkenylenegroup of 2 to 6, more preferably 2 to 5, carbon atoms, containingone--C═C-- bond.

The term "alkynyl" as used herein refers to a branched or unbranchedhydrocarbon group of 2 to 24 carbon atoms containing at leastone--C.tbd.C-- bond, such as ethynyl, n-propynyl, isopropynyl,n-butynyl, isobutynyl, t-butynyl, octynyl, decynyl and the like.Preferred alkynyl groups herein contain 2 to 12 carbon atoms. The term"lower alkynyl" intends an alkynyl group of 2 to 6 carbon atoms,preferably 2 to 4 carbon atoms, and one --C.tbd.C-- bond.

The term "alkynylene" refers to a difunctional branched or unbranchedhydrocarbon chain containing from 2 to 24 carbon atoms and at least onecarbon-carbon triple bond. "Lower alkynylene" refers to an alkynylenegroup of 2 to 6, more preferably 2 to 5, carbon atoms, containingone--C.tbd.C-- bond.

The term "alkoxy" as used herein intends an alkyl group bound through asingle, terminal ether linkage; that is, an "alkoxy" group may bedefined as --OR where R is alkyl as defined above. A "lower alkoxy"group intends an alkoxy group containing one to six, more preferably oneto four, carbon atoms.

The term "aryl" as used herein refers to an aromatic species containing1 to 5 aromatic rings, either fused or linked, and either unsubstitutedor substituted with 1 or more substituents typically selected from thegroup consisting of --(CH₂) _(x) --NH₂, --(CH₂)_(x) --COOH, --NO₂,halogen and lower alkyl, where x is an integer in the range of 0 to 6inclusive as outlined above. Preferred aryl substituents contain 1 to 3fused aromatic rings, and particularly preferred aryl substituentscontain 1 aromatic ring or 2 fused aromatic rings. The term "aralkyl"intends a moiety containing both alkyl and aryl species, typicallycontaining less than about 24 carbon atoms, and more typically less thanabout 12 carbon atoms in the alkyl segment of the moiety, and typicallycontaining 1 to 5 aromatic rings. The term "aralkyl" will usually beused to refer to aryl-substituted alkyl groups. The term "aralkylene"will be used in a similar manner to refer to moieties containing bothalkylene and aryl species, typically containing less than about 24carbon atoms in the alkylene portion and 1 to 5 aromatic rings in thearyl portion, and typically aryl-substituted alkylene. Exemplary aralkylgroups have the structure --(CH₂)_(j) --Ar wherein j is an integer inthe range of 1 to 24, more typically 1 to 6, and Ar is a monocyclic arylmoiety.

The term "arylene" refers to a difunctional aromatic moiety; "monocyclicarylene" refers to a cyclopentylene or phenylene group. These groups maybe substituted with up to four ring substituents as outlined above.

The term "heterocyclic" refers to a five- or six-membered monocyclicstructure or to an eight- to eleven-membered bicyclic heterocycle whichis either saturated or unsaturated. Each heterocycle consists of carbonatoms and from one to four heteroatoms selected from the groupconsisting of nitrogen, oxygen and sulfur. As used herein, the terms"nitrogen heteroatoms" and "sulfur heteroatoms" include any oxidizedform of nitrogen and sulfur, and the quaternized form of any basicnitrogen. Examples of heterocyclic groups include piperidinyl,morpholinyl and pyrrolidinyl.

"Halo" or "halogen" refers to fluoro, chloro, bromo or iodo, and usuallyrelates to halo substitution for a hydrogen atom in an organic compound.Of the halos, chloro and fluoro are generally preferred.

"Hydrocarbyl" refers to unsubstituted and substituted hydrocarbylradicals containing 1 to about 20 carbon atoms, including branched orunbranched, saturated or unsaturated species, such as alkyl groups,alkenyl groups, aryl groups, and the like. The term "lower hydrocarbyl"intends a hydrocarbyl group of one to six carbon atoms, preferably oneto four carbon atoms. "Cyclometallated hydrocarbyl" refers to a cyclichydrocarbyl group containing one or more metal atoms, typically a singlemetal atom.

"Optional" or "optionally" means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where said event or circumstance occurs and instances where itdoes not. For example, the phrase "optionally substituted alkylene"means that an alkylene moiety may or may not be substituted and that thedescription includes both unsubstituted alkylene and alkylene wherethere is substitution.

A "heterogeneous" catalyst as used herein refers to a catalyst which issupported on a carrier, typically although not necessarily a substratecomprised of an inorganic, solid, particulate porous material such assilicon and/or aluminum oxide.

A "homogeneous" catalyst as used herein refers to a catalyst which isnot supported but is simply admixed with the initial monomericcomponents in a suitable solvent.

The term "multimodal molecular weight distribution" as used herein, andas alluded to above, refers to a polymer composition having two or moremolecular weight distributions, as may be determined, for example, bythe appearance of two or more peaks in a gel permeation chromatogram.Unless otherwise specified herein, the term "multimodal" is intended toencompass the term "bimodal." By the process of the invention, polymercompositions having a "multimodal" molecular weight distribution can begenerated using a multimolecular metallocene catalyst in whichpolymerization takes place at different propagation rates at differentactive sites within the catalyst structure, or wherein the differentactive sites give rise to different termination rates, and/or whereinthe different active sites have different responses to H₂ (or otherchain transfer agents). While the term"multimodality" generally refersto a multimodal molecular weight distribution, it should be emphasizedthat a polymer composition can also be "multimodal" with respect tocompositional distribution, tacticity distribution, long-chain branchingdistribution, or the like.

As used herein all reference to the Periodic Table of the Elements andgroups thereof is to the version of the table published by the Handbookof Chemistry and Physics, CRC Press, 1995, which uses the IUPAC systemfor naming groups.

The Catalysts:

The catalysts used in the polymerization process of the invention are,as explained above, metallocenes having two or more distinct andchemically different active sites. Preferred catalysts are representedby the formula B(Z)_(q) as shown in structure (I) ##STR2## wherein B, Z,Q, M, X, Y, R, R¹, x, y, m and n are as defined previously.

B, as noted earlier herein, is a covalent bridging group which iscomprised of a hydrocarbyl radical optionally containing a Group IVBelement, a Group VB element, or both. The bridging group is capable ofbinding n_(max) substituents through single covalent bonds; n_(max) inturn determines q, the number of Z substituents present in the complex.That is, q is an integer in the range of 2 to q_(max), wherein q_(max)is equal to 1/2n_(max) when n_(max) is an even number, and 1/2(n_(max)-1) when n is an odd number. Thus, when n_(max) is 6, up to three Zgroups may be present; when n_(max) is 5, one or two Z groups may bepresent; when n_(max) is 4, again, the maximum number of Z groups is 2.Preferred B groups are C₁ -C₁₂ hydrocarbyl radicals optionallycontaining a Group IVB element and/or a Group VB element, andparticularly preferred B groups are C₁ -C₆ hydrocarbyl groups, e.g.,ethylene, dimethylethylene, propylene, etc., and silicon.

The cyclopentadienyl moiety, as shown, is optionally substituted with Rand R¹ groups. Specifically, the integers x and y are independently 0,1, 2, 3 or 4, with the proviso that the sum of x and y cannot exceed 4;preferably, x and y are independently 0, 1 or 2, and most preferably are0 or 1. R and R¹ can be halogen, C₁ -C₂₄ hydrocarbyl, eitherunsubstituted or substituted with one or more halogen atoms, lower alkylgroups and/or Group IVB elements. Alternatively, when an R and an R¹substituent are both present, and ortho to each other on thecyclopentadienyl ring, they may together form a five- or six-memberedcyclic structure. This cyclic structure may be unsubstituted orsubstituted with a halogen or C₁ -C₂₄ hydrocarbyl group as explainedabove. Preferred R and R¹ substituents are halogen and C₁ -C₁₂ alkyl;complexes wherein R and R¹ are ortho to each other and linked to form acyclopentadienyl or indenyl group, either unsubstituted or substitutedwith halogen and/or lower alkyl moieties, are also preferred.Particularly preferred R and R¹ groups are halogen and lower alkyl;complexes wherein R and R¹ are ortho to each other and linked to form acyclopentadienyl ring optionally substituted with a lower alkyl groupare also particularly preferred.

Q is cyclopentadienyl, indenyl, fluorenyl, indolyl or aminoboratobenzyl,and may be unsubstituted or substituted with R and/or R¹ substituents asabove. Alternatively, Q is J(R²) _(z-2) wherein J is an element with acoordination number of three from Group VB or an element with acoordination number of two from Group VIB, R² is selected from the groupconsisting of hydrogen, C₁ -C₂₄ hydrocarbyl, C₁ -C₂₄ hydrocarbylsubstituted with one or more, typically one to twelve, halogen atoms,and C₁ -C₂₄ alkoxy, and z is the coordination number of J. In addition,Q substituents on different Z groups may be linked through a C₁ -C₂₄hydrocarbylene bridge. Typically, although not necessarily, such alinkage is between different R² groups. Preferred Q substituents arecyclopentadienyl, indenyl, fluorenyl, aminoboratobenzyl or J(R²)_(z-2)wherein J is nitrogen, phosphorus, oxygen or sulfur, and R² is C₁ -C₁₂alkyl optionally substituted with one or more, typically one to six,halogen atoms. Particularly preferred Q groups are NR² moieties whereinR² is lower alkyl or phenyl.

M is a Group IIIA element, a Group IVA element, a Group VA element, alanthanide, or an actinide. Preferred Group IVA elements are Zr, Hf andTi, with Zr particularly preferred.

X is hydride, halide, alkoxy, amido, or substituted or unsubstituted C₁-C₂₄ hydrocarbyl; if substituted, the substituents areelectron-withdrawing groups such as a halogen atom, an alkoxy group, orthe like, or the substituents may be a Group IVB element. If two or moreX moieties are present in the complex, they may be the same ordifferent. When two or more X substituents are present, any two maytogether form an alkylidene olefin (i.e., ═CR₂ wherein R is hydrogen orhydrocarbyl, typically lower alkyl), acetylene, or a five- orsix-membered cyclic hydrocarbyl group. Preferred X moieties are hydride,amido, C₁ -C₁₂ alkyl, and C₁ -C₁₂ alkyl substituted with one or morehalogen and/or alkoxy groups, typically one to six such groups, and C₁-C₁₂ alkyl substituted with a Group IVB element. Particularly preferredX substituents are hydride, amido and lower alkyl.

The integer "m" defines the number of X substituents bound to theelement M, and is 1, 2, 3 or 4. Preferably, m is 1 or 2. When M isboron, m, clearly, cannot exceed 1.

Y is a neutral Lewis base, preferably diethylether, tetrahydrofuran,dimethylaniline, aniline, trimethylphosphine, or n-butylamine.Diethylether and tetrahydrofuran are most preferred.

The integer "n" defines the number of Y substituents bound to theelement M, and is 0, 1, 2 or 3. Preferably n is 0 or 1. When M is aGroup IIIA element m is 1, as noted above, and n is necessarily 0. WhenM is a Group IVB element, the sum of m and n cannot, clearly, exceed 2.

The number of Z groups bound to B is shown in the structure of formula(I) as q, which is in turn defined by "_(max) " as explained above. Inthe preferred complexes herein, q is 2 or 3, and is most typically 2.Because the present catalysts call for the presence of at least twodistinct and chemically different active sites, the Z groups bound to Bare structurally different. That is, two of the metal atoms M may bedifferent, or, when all of the metal atoms in the complex are the same,the substituents bound to one are different from those bound to another.

Examples of specific metallocene catalysts within the purview of theinvention include, but are not limited to, the following: ##STR3##

In addition, Table 1 illustrates representative substituents in atypical metallocene catalyst which may be used in conjunction with thepresent polymerization process:

                                      TABLE 1                                     __________________________________________________________________________    B            Ar*             Q         X      Y        M     Q                __________________________________________________________________________    silyl        cylcopentadienyl                                                                              t-butylamide                                                                            hydride                                                                              diethylether                                                                           zirconium                                                                           2                disilyl      methylcyclopentadienyl                                                                        phenylamido                                                                             methyl tetrahydrofuran                                                                        hafnium                                                                             3                germanyl     1,2-dimethylcyclopentadienyl                                                                  p-n-butylphenylamido                                                                    ethyl  dimethylaniline                                                                        titanium                                                                            4                ammonium     1,3-dimethylcyclopentadienyl                                                                  cyclohexylamido                                                                         phenyl aniline                         phosphonium  indenyl         perflurophenylamido                                                                     n-propyl                                                                             trimethylphosphine              1 #STR4##    1,2-diethylcyclopentadienyl tetramethylcyclopentadienyl                       ethylcyclopentadienyl                                                                         n-butylamido methylamido ethylamido                                                     isopropyl n-butyl                                                                    n-butylamine                    2 #STR5##    n-butylcyclopentadienyl cyclohexylmethylcyclopentadienyl                      n-octylcyclopentadienyl                                                                       n-propylamido isopropylamido                                                            isoamyl hexyl isobutyl                 3 #STR6##    β-phenylpropylcyclopentadienyl tetrahydroindenyl                         propylcyclopentaadienyl                                                                       t-butylphosphido ethylphosphido                                               phenylphosphido                                                                         heptyl octyl nonyl                     4 #STR7##    t-butylcyclopentadienyl benzylcyclopentadienyl                                1,2-dichlorocyclopentadienyl                                                                  cyclohexylphosphido oxo methoxide                                                       decyl cetyl ethylidene                 5 #STR8##    1,3-dichlorocyclopentadienyl methylindenyl                                    trifluoromethylcyclopentadienyl                                                               sulfido ethoxide methylthio                                                             methylidene propylidene chloro         6 #STR9##    1,2-difluorocyclopentadienyl fluorenyl methylfluorenyl                                        ethylthio cyclopentadienyl indenyl               7 #STR10##   octahydrofluorenyl indolyl methylindolyl                                                      fluorenyl aminoboratobenzyl                      8 #STR11##   2-methyl-4-phenyl indenyl 2-methyl-4-napthyl indenyl                          2-methyl-4-butyl indenyl                                         __________________________________________________________________________

In Table 1, "Ar" represents the substituent ##STR12## as shown in thestructure of Formula (I). The Catalyst System Used:

The process of the invention typically involves using the metallocenecatalyst in conjunction with a conventional catalyst activator as willbe appreciated by those skilled in the art. Suitable catalyst activatorsinclude metal alkyls, hydrides, alkylhydrides, and alkylhalides, such asalkyllithium compounds, dialkylzinc compounds, trialkyl boron compounds,trialkylaluminum compounds, alkylaluminum halides and hydrides, andtetraalkylgermanium compounds. Specific examples of useful activatorsinclude n-butyllithium, diethylzinc, di-n-propylzinc, triethylboron,triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum,ethylaluminum dichloride, dibromide and dihydride, isobutyl aluminumdichloride, dibromide and dihydride, di-n-propylaluminum chloride,bromide and hydride, diisobutylaluminum chloride, bromide and hydride,ethylaluminum sesquichloride, methylaluminoxane ("MAO"),hexaisobutylaluminoxane, tetraisobutylaluminoxane,polymethylaluminoxane, tri-n-octylaluminum, tetramethylgermanium, andthe like. Other activators which are typically referred to as ioniccocatalysts may also be used; such compounds include, for example, (C₆H₆)₃ ⁺, C₆ H₅ --NH₂ CH₃ ⁺, and tetra(pentafluorophenyl)boron. Mixturesof activators may, if desired, be used.

For liquid phase or slurry polymerization, the catalyst and activatorare generally mixed in the presence of inert diluents such as, forexample, aliphatic or aromatic hydrocarbons, e.g., liquified ethane,propane, butane, isobutane, n-butane, n-hexane, isooctane, cyclohexane,methylcyclohexane, cyclopentane, methylcyclopentane, cycloheptane,methylcycloheptane, benzene, ethylbenzene, toluene, xylene, kerosene,Isopar® M, Isopar® E, and mixtures thereof. Liquid olefins or the likewhich serve as the monomers or comonomers in the polymerization processmay also serve as the diluent; such olefins include, for example,ethylene, propylene, butene, 1-hexene and the like. The amount ofcatalyst in the diluent will generally be in the range of about 0.01 to1.0 mmoles/liter, with activator added such that the ratio of catalystto activator is in the range of from about 10:1 to 1:2000, preferably inthe range of from about 1:1 to about 1:200, on a molar basis.

Various additives may be incorporated into the mixture; particularlypreferred additives are neutral Lewis bases such as amines, anilines andthe like, which can accelerate the rate of polymerization.

Preparation of the catalyst/activator/diluent mixture is normallycarried out under anhydrous conditions in the absence of oxygen, attemperatures in the range of from about -90° C. to about 300° C.,preferably in the range of from about -10° C. to about 200° C.

The catalyst, activator and diluent are added to a suitable reactionvessel, in any order, although, as noted above, the catalyst andactivator are usually mixed in the diluent and the mixture thus preparedthen added to the reactor.

The Polymerization Process:

Polymerization is carried out by contacting the selected monomer withthe catalyst and catalyst activator at a suitable temperature atreduced, elevated or atmospheric pressure, under an inert atmosphere,for a time effective to produce the desired polymer composition. Thecatalyst may be used as is or supported on a suitable support. In oneembodiment, the metallocene compound is used as a homogeneous catalyst,i.e., as an unsupported catalyst, in a gas phase or liquid phasepolymerization process. A solvent may, if desired, be employed. Thereaction may be conducted under solution or slurry conditions, in asuspension using a perfluorinated hydrocarbon or similar liquid, in thegas phase, or in a solid phase powder polymerization.

Liquid phase polymerization generally involves contacting the monomerwith the catalyst/activator mixture in the polymerization diluent, andallowing reaction to occur under polymerization conditions, i.e., for atime and at a temperature sufficient to produce the desired polymerproduct. Polymerization may be conducted under an inert atmosphere suchas nitrogen, argon, or the like, or may be conducted under vacuum.Preferably, polymerization is conducted in an atmosphere wherein thepartial pressure of reacting monomer is maximized. Liquid phasepolymerization may be carried out at reduced, elevated or atmosphericpressures. In the absence of added solvent, i.e., when the monomerserves as the diluent, elevated pressures are preferred. Typically, highpressure polymerization in the absence of solvent is carried out attemperatures in the range of about 180° C. to about 300° C., preferablyin the range of about 250° C. to about 270° C., and at pressures on theorder of 200 to 20,000 atm, typically in the range of about 1000 to 3000atm. When solvent is added, polymerization is generally conducted attemperatures in the range of about 150° C. to about 300° C., preferablyin the range of about 220° C. to about 250° C., and at pressures on theorder of 10 to 2000 atm.

Polymerization may also take place in the gas phase, e.g., in afluidized or stirred bed reactor, using temperatures in the range ofapproximately 60° C. to 120° C. and pressures in the range ofapproximately 10 to 1000 atm.

The monomer or comonomers used are addition polymerizable monomerscontaining one or more degrees of unsaturation. Olefinic or vinylmonomers are preferred, and particularly preferred monomers areα-olefins having from about 2 to about 20 carbon atoms, such as, forexample, linear or branched olefins including ethylene, propylene,1-butene, 3-methyl-1-butene, 1,3-butadiene, 1-pentene,4-methyl-1-pentene, 1-hexene, 4-methyl-1-hexene, 1,4-hexadiene,1,5-hexadiene, 1-octene, 1,6-octadiene, 1-nonene, 1-decene,1,4-dodecadiene, 1-hexadecene, 1-octadecene, and mixtures thereof.Cyclic olefins and diolefins may also be used; such compounds include,for example, cyclopentene, 3-vinylcyclohexene, norbornene,5-vinyl-2-norbornene, 5-ethylidene-2-norbornene, dicyclopentadiene,4-vinylbenzocyclobutane, tetracyclododecene,dimethano-octahydronaphthalene, and 7-octenyl-9-borabicyclo-(3,3,1)nonane. Aromatic monomers which may be polymerized using the novelmetallocenes include styrene, o-methylstyrene, m-methylstyrene,p-methylstyrene, p-tert-butylstyrene, m-chlorostyrene, p-chlorostyrene,p-fluorostyrene, indene, 4-vinylbiphenyl, acenaphthalene, vinylfluorene,vinylanthracene, vinylphenanthrene, vinylpyrene and vinylchrisene. Othermonomers which may be polymerized using the present catalysts includemethylmethacrylate, ethylacrylate, vinyl silane, phenyl silane,trimethylallyl silane, acrylonitrile, maleimide, vinyl chloride,vinylidene chloride, tetrafluoroethylene, isobutylene, carbon monoxide,acrylic acid, 2-ethylhexylacrylate, methacrylonitrile and methacrylicacid.

In gas and slurry phase polymerizations, the catalyst is used in aheterogeneous process, i.e., supported on an inert inorganic substrate.Conventional materials can be used for the support, and are typicallyparticulate, porous materials; examples include oxides of silicon andaluminum, or halides of magnesium and aluminum. Particularly preferredsupports from a commercial standpoint are silicon dioxide and magnesiumdichloride.

The polymeric product resulting from the aforementioned reaction may berecovered by filtration or other suitable techniques. If desired,additives and adjuvants may be incorporated into the polymer compositionprior to, during, or following polymerization; such compounds include,for example, pigments, antioxidants, lubricants and plasticizers.

As explained earlier herein, the invention enables preparation ofpolymer compositions that are bimodal or multimodal in nature,typically, but not necessarily, having a multimodal molecular weightdistribution. The catalysts used herein contain two or more active sitesat which propagation rates differ, or which have different temperaturesensitivities and/or H₂ responsiveness or the like. In this way, thetype and degree of multimodality in the polymeric product can becontrolled as desired. Bimodal or multimodal polymer compositions areuseful insofar as rheological behavior, mechanical strength andelasticity can be improved relative to corresponding compositions whichare not multimodal.

Catalyst Synthesis:

The catalysts used herein are synthesized using any one of severaltechniques. In general, the catalysts may be prepared using relativelysimple and straightforward synthetic processes which enable precisecontrol of the final metallocene structure and the active sitescontained therein.

One suitable synthesis involves the use of a halogenated compoundB(Hal)_(2q) as a starting material (wherein B and q are as definedearlier herein and "Hal" represents a halogen atom). The compound iscontacted with an alkali metal salt of an aromatic compound Ar,containing one to three cyclopentadienyl rings, either substituted orunsubstituted, to provide an intermediate Ar_(q) B(Hal)_(q). (When it isdesired that the end product contain different aromatic groups,successive reaction with different aromatic salts is carried out, i.e.,B(Hal)_(2q) is first reacted with an alkali metal salt of a firstaromatic species Ar1, then with an alkali metal salt of a secondaromatic species Ar2, and the like.) This intermediate is then used toprepare a ligand Ar_(q) B[J(R²)_(z-2) H]_(q) wherein J, R² and z are asdefined previously, by reaction with an alkali metal salt of J(R²)_(z-2)H. (Again, for an end product to contain different J(R²)_(z-2) species,successive reaction is carried out with alkali metal salts of differentJ(R²)_(z-2) H groups.) The ligand is deprotonated and then reacted witha halogenated metal compound M(Hal)_(y), wherein y represents the numberof halogen atoms corresponding to the oxidation state of M. In such acase, the metal atoms in the complex will be identical to one another.

In an alternative method, a starting material B(Hal)₄ is caused to reactwith an alkali metal salt of an aromatic compound Ar containing one, twoor three cyclopentadiene rings each optionally substituted with x "R"substituents and y "R¹ " substituents, to give an intermediate havingthe formula Ar₂ B(Hal)₂. This intermediate is then caused to react witha bridging compound comprising a C₁ -C₁₂ linear or branched alkylenelinker L substituted with two primary amine substituents, to provide aligand Ar₂ BL₂. As above, the ligand is deprotonated and thensuccessively reacted with first and second halogenated metal compoundsM(Hal)y, wherein the metal atoms in each of the metal compounds aredifferent, to provide a metallocene catalyst having the structure offormula (I), wherein the metal atoms in each Z substituent aredifferent.

For end products wherein "Q" is other than J(R²)_(z-2), a similarprocedure is carried out, i.e., alkali metal salts of compounds havingthe general structure Q-H are used in place of alkali metal salts ofJ(R²)_(z-2).

Alternative transmetalation techniques are also possible, as will beappreciated by those skilled in the art. For example, Huttenhofer etal., "Substituted Silastannatetrahydro-s-indacenes as CyclopentadienylTransfer Agents in the Synthesis of Silanediyl-Bridged ZirconoceneComplexes," Organometallics 15:4816-4822 (1996), describes a method forpreparing metallocenes using substitutedsilastannatetrahydro-s-indacenes as cyclopentadienyl transfer agents.The Huttenhofer et al. and other methods can be used herein as well.

EXPERIMENTAL

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how toprepare and use the metallocene catalysts as disclosed herein to providea polymer composition having a multimodal molecular weight distribution.Efforts have been made to ensure accuracy with respect to numbers (e.g.,amounts, temperature, etc.) but some errors and deviations should beaccounted for. Unless indicated otherwise, parts are parts by weight,temperature is in ° C. and pressure is at or near atmospheric.

All patents, patent applications, journal articles and other referencesmentioned herein are incorporated by reference in their entireties.

Examples 1 through 9 describe methods for synthesizing variousmetallocene catalysts; Example 10 describes a procedure for using thecatalysts in the preparation of polyethylene; and Example 11 describesthe procedure used to evaluate the bimodality of the polymer compositionprepared using the catalyst of Example 4.

EXAMPLE 1 ##STR13##

The catalyst shown was prepared as follows:

Tetramethyl cyclopentadiene (4.7 g) was dissolved in 102 mL THF andcooled to -78° C. n-Butyllithium (18.2 mL of 2.2M in hexane) was addeddropwise. The mixture was allowed to warm to room temperature andstirred for 1 h. The resulting suspension was then cooled to -30° C. and2.25 mL of SiCl₄ was added over 10 minutes. The mixture was allowed towarm to room temperature to give a colorless solution. The solution wasthen stirred at room temperature overnight. The solution was thenfiltered and concentrated to dryness. The solid was then extracted withpentane and filtered. The pentane was removed to give a colorless solid(6.20 g of bis-tetramethylcyclopentadienyl silicon dichloride).(Analytically pure samples could be obtained by recrystallizing from aconcentrated pentane solution.)

Bis-tetramethyl cyclopentadienyl silicon dichloride (2.40 g) was thendissolved in 45 mL THF. To this solution lithium cyclohexylamide (1.49 gin portions) was added. The solution was stirred overnight and thesolvents then removed. The solid was extracted with pentane, filtered,and the pentane removed. Yield: 3.30 g of light yellow biscyclohexylamido bis-tetra-methyl cyclopentadienyl silane.

Bis-cyclohexylamido bis-tetramethylcyclopentadienyl silane (3.29 g) wasdissolved in 70 mL of Et₂ 0 and cooled to 0° C. n-Butyllithium (3.6 mLof 10 M in hexane) was added slowly. The mixture was allowed to warm toroom temperature and stirred overnight. The solvents were removed toyield a yellow solid. The yellow solid was slurried in pentane andfiltered. The solid was washed three times with pentane to give 2.30 gof an off-white solid ##STR14##

Zirconium tetrachloride (560 mg) and hafnium tetrachloride (770 mg) wereslurried in 65 mL diethyl ether. To that slurry was added 1.18 g of theoff-white solid prepared above (gradually, over a 15 minute period). Themixture was diluted with 10 mL of diethyl ether (to wash the solidaddition funnel). The mixture was allowed to stir for 18 h. The solventwas then removed. The solid was extracted with 20 mL toluene andfiltered. The toluene was removed to yield 1.96 g of a pale yellowpowder. NMR indicated the expected mixture of products: the Zr-Zr, Zr-Hfand Hf-Hf dimetallated products.

EXAMPLE 2 ##STR15##

The catalyst shown was prepared as follows:

Bis-tetramethylcyclopentadienyl silicon dichloride was prepared asdescribed in Example 1. Lithium-t-butylamide was slurried in 50 mLdiethyl ether. Bis-tetramethyl cyclopentadienyl silicon dichloride (1.88g) was added slowly. The mixture was allowed to stir overnight. Thesolvent was removed and the mixture extracted with pentane and filtered.Removal of pentane gave a yellow oil. The yellow oil was dissolved in100 mL diethyl ether and cooled to 0° C. n-Butyllithium (3.0 mL of 10Min hexane) was added. The reaction was allowed to warm to roomtemperature and stirred overnight. The solvent was removed, and theremaining solid was slurried in pentane and filtered to give 0.70 g ofcolorless solid ##STR16##

Zirconium tetrachloride (744 mg) was suspended in 60 mL diethyl ether.The 700 mg of colorless solid prepared above was added slowly to thereaction mixture. The solid addition fnnnel was then washed with 10 mLof diethyl ether which was added to the reaction mixture. The mixturewas allowed to stir overnight and the solvent was then removed. Thesolid was extracted with toluene and then filtered. The toluene wasremoved to give 1.06 g of a golden colored solid.

EXAMPLE 3 ##STR17##

The catalyst shown was prepared as follows:

The ligand was prepared as in Example 1.

Zirconium tetrachloride (932 mg) was slurried in 70 mL diethyl ether. Tothat slurry was added slowly over 20 minutes 981 mg of ##STR18## Thereaction mixture was stirred for 24 h. The solvent was removed and thesolid extracted with toluene. The toluene solution was filtered and thesolvent removed to isolate 1.44 g of a light yellow crystalline solid.

EXAMPLE 4 ##STR19##

The catalyst shown was prepared as follows:

The ligand was prepared as in Example 1.

Hafnium tetrachloride was slurried in 70 mL diethyl ether. To thatslurry was added slowly over 10 min 0.98 g of ##STR20## The mixture wasallowed to stir for 24 h. The solvent was then removed, and theremaining solid was extracted with toluene. The toluene was removed toisolate a light yellow solid (1.74 g).

EXAMPLE 5 ##STR21##

The catalyst shown was prepared as follows: The ligand was prepared asin Example 1. TiCl₃. 3THF was dissolved in 60 mnL THF and 736 mg of theligand ##STR22## was added. The mixture was allowed to stir for 1/2 hourgiving a purple solution. To that solution 473 mg of AgCl was added. Thesolution was allowed to stir for 1 h. The solvent was evaporated fromthe red-brown mixture, and the resulting solid was extracted withpentane and filtered. The solution was then concentrated and cooled tocrystallize the reddish yellow product. Repeated concentrations andcrystallizations allowed the recovery of several crops of the product(0.60 g combined).

An alternative synthesis of this catalyst is to slurry 1.34 g of TiCl₄.2THF in toluene (70 mL). To this mixture 0.88 g of the ligand ##STR23##was added slowly. The reaction mixture turned brown quickly. The mixturewas allowed to stir for 4 days and then filtered. The toluene wasremoved, and the resulting solid was extracted in pentane and filtered.The pentane was removed to give a reddish-yellow solid.

EXAMPLE 6 ##STR24##

The catalyst shown was prepared as follows:

The catalyst prepared by the first method of Example 5 was used as thestarting material in this example.

The catalyst of Example 5 (0.49 g) was dissolved in THF and cooledto-30° C. CH₃ MgCl (0.93 mL, 3M in THF) was added slowly. The reactionwas allowed to warm to room temperature and stirred for 1 h. The solventwas removed and the solid extracted with pentane. The pentane solutionwas filtered and the solvent removed to yield 0.32 g of brown solid.

EXAMPLE 7 ##STR25##

The catalyst shown was prepared as follows:

The ligand ##STR26## was prepared as in Example 2.

TiCl₃. 3THF (112g) was slurried in 50 mL of THF. The ligand (0.66 g) wasslowly added to this reaction mixture. The deep purple mixture wasstirred for 1.5 h and then 0.50g of AgCl was added. The mixture wasallowed to continue to stir for 3 h at which time it turned reddishyellow. The mixture was filtered and the solvent removed. The solid wasredissolved in toluene, filtered, and the toluene removed. This solidwas then slurried in pentane, filtered, and the pentane removed to givea small amount of reddish yellow product.

EXAMPLE 8 ##STR27##

The catalyst shown was prepared as follows:

Indene (5.81 g) was dissolved in 25 mL of toluene and 20 mL of 3M EtMgBrin diethyl ether was added. The mixture was slowly heated until theether was distilled off. Then the mixture was heated at toluene refluxfor 5.5 h. The mixture was allowed to cool and the toluene removed undervacuum. The solid was dried at 80-90° C. for 1/2 h. The solid was washedwith hexanes. The indenyl Grignard was then slurried in 200 mL diethylether and cooled to -20° C. to -30° C. SiCl₄ (2.9 mL in 100 mL Et₂ 0)was added slowly over ˜1/2 h. The suspension was allowed to warm to roomtemperature and then heated to reflux. The mixture was held at refluxovernight and then allowed to cool. The Et₂ 0 was removed in vacuum. Thesolid was stirred in hexanes for 2 h and filtered. The hexanes wereremoved by vacuum to give 6.63 g of light yellow solid: dichloro,diindenyl silane.

Dichloro, diindenyl silane (6.45 g) was slurried in 20 mL hexanes and 10mL diethyl ether. The mixture was cooled to 0° C. and 9.2 mL ofcyclohexylamine in 10 mL hexanes was added slowly. The mixture washeated to reflux for 1 h, cooled and filtered. The solvent was removedto give di(cyclohexylamino)diindenyl silane as a tan solid (7.60 g).

Di(cyclohexylamino)diindenyl silane (7.60 g) was dissolved in 140 mL ofdiethyl ether. n-Butyllithium (8.0 mL of 10 M in hexane) was added. Themixture was allowed to stir for 2 days. The diethyl ether was removed.The solid was extracted with pentane and filtered. The pentane wasremoved yielding a colorless solid (8.03 g): ##STR28##

A slurry in toluene (60 mL) was made of 0.96 g of the ligand shown and1.34 g of TiCl₃. 2THF. The mixture was allowed to stir for 6 days. Theslurry was filtered and the toluene removed to give a red-brown solid ofthe catalyst (0.84 g).

EXAMPLE 9 ##STR29##

The catalyst shown was prepared as follows:

Dichloro, diindenyl silane was prepared as in Example 8. n-Propylamine(0.5 mnL) was dissolved in 25 mL of hexanes and cooled to 0° C.Dichloro, diindenylsilane (28 g) in 25 mL of hexanes was slowly added.The addition funnel was washed with 5 mL of diethyl ether which wasadded to the reaction mixture. The reaction mixture was heated at refluxfor 1 h. The mixture was allowed to cool and filtered. The solvent wasremoved to give 7.53 g of tan oil.

The tan oil (7.45 g) prepared above ##STR30## was dissolved in a mixtureof 55 mL pentane and 15 mL diethyl ether. n-Butyllithium (8.2 mL of 10 Min hexanes) was added dropwise. The reaction was highly exothermic. Thesuspension was refluxed for 2 h and 10 addition mL of diethyl etheradded. The mixture was filtered and the solid was washed with a 1:1mixture of diethyl ether and pentane. 7.05 g of ##STR31## werecollected.

TiCl₄. 2THF (1.01 g) and 1.20 g of the ligand shown were mixed and 70 mLof toluene added. The reaction mixture turned reddish brown. The mixturewas allowed to stir for 24 h. Then additional TiCl₄. 2THF was dissolvedin 25 mL toluene and added to the reaction mixture. The mixture wasallowed to stir for 5 days. The mixture was filtered and the solventremoved. The solid was extracted with pentane and filtered. The pentanewas removed to give 1.46 g of brown solid.

EXAMPLE 10

The metallocene compounds prepared in Examples 1 through 9 were used aspolymerization catalysts in the preparation of polyethylene ("PE"). Theamount of catalyst used and reaction temperature are in Table 2.Standard ethylene polymerization conditions were used, as follows:Polymerizations were conducted in a 300 mnL autoclave reactor. Methylaluminoxane (MAO) was used as co-catalyst with total Al/M ratio equal to1000 (with the exception of the comparison polymerization with Cp₂ ZrCl₂which was run with Al/M=2000). Prior to initiation of polymerization,the reactors were loaded with 160 mL of toluene and the MAO. Thereactors were heated to the desired reaction temperature and pressurizedwith ethylene to 40 psig. The reactors were configured to maintain theset pressure and temperature during the polymerization reaction. Thereaction was initiated by injection of the catalyst. The reactions wererun for 30 minutes and terminated by injection of acidified methanol (2%HCl). The polymer was removed from the reactor and washed withadditional acidified methanol, aqueous NaHCO₃, water and acetone. Thepolymer was dried in a vacuum oven overnight.

Results are set forth in Table 2:

                                      TABLE 2                                     __________________________________________________________________________    Catalyst            Reaction                                                                             Catalyst Activity                                                                           Amount of PE                         Example #                                                                              Amount of Catalyst Used                                                                  Temperature                                                                          PE: metallocene                                                                       PE: metal                                                                           Isolated                             __________________________________________________________________________    1        3.4 μmol; 3 mg                                                                        70° C.                                                                        3,080   10,000                                                                              4.62 g.                              2        4.5 μmol: 3.3 mg                                                                      70° C.                                                                        2,691   10,850                                                                              4.44 g.                              3        2.5 μmol: 2.0 mg                                                                      r.t.   2,440   10,517                                                                              2.44 g.                              3        2.5 μmol: 2.0 mg                                                                      70° C.                                                                        2,700   11,638                                                                              2.70 g.                              3        3.5 μmol: 2.8 mg                                                                      105° C.                                                                       3,757   16,194                                                                              5.26 g.                              4        3.1 μmol: 3.0 mg                                                                      r.t.     193     521 0.29 g.                              4        3.1 μmol: 3.0 mg                                                                      70° C.                                                                        1,733   4,672 2.60 g.                              4        3.1 μmol: 3.0 mg                                                                      115° C.                                                                       1,573   4.241 2.36 g.                              4        3.1 μmol: 3.0 mg                                                                      70° C., 20 min                                                                --      --    2.22 g.                              5        4.2 μmol: 3.0 mg                                                                      70° C.                                                                          733   5,353 1.10 g.                              5        2.1 μmol: 1.5 mg                                                                      70° C.                                                                          320   2,336 0.24 g.                              5        2.8 μmol: 2.0 mg                                                                      70° C.                                                                          260   1,898 0.26 g.                              5        1.4 μmol: 1.0 mg                                                                      70° C.                                                                          840   6,131 0.42 g.                              5        2.8 μmol: 2.0 mg                                                                      r.t.    1280   9,343 1.28 g.                              6        <8 μmol r.t.   --      --    little                               7        4.6 μmol: 3.0 mg                                                                      70° C.                                                                        --      --    0                                    Cp.sub.2 ZrCl.sub.2 (standard)                                                         5.0 μmol, 1.5 mg                                                                      70° C.                                                                        11,267  36,112                                                                              8.45 g                               8        1.4 μmol, 1.0 mg                                                                      70° C.                                                                        560; 720                                                                              3972; 5106                                                                          0.28 g., 0.36 g.                     9        1.6 μmol, 1.0 mg                                                                      70° C.                                                                        480+     3057 0.24 g                               __________________________________________________________________________

EXAMPLE 11

The polyethylene composition produced using the procedure of Example 10and the catalyst of Example 4 was evaluated using gel permeationchromatography. FIG. 1 shows a typical bimodal distribution obtained.FIG. 2 shows the molecular weight distribution obtained at apolymerization temperature of 70° C.; as may be seen, the distributionof FIG. 2 is monomodal. Thus, reaction parameters such as temperaturecan be used to control the modality of the polymer composition obtained.Other catalysts as described herein are expected to work in a similarmanner, providing multimodal compositions as desired.

I claim:
 1. A method for preparing a polymer composition having amultimodal molecular weight distribution, comprising contacting, underpolymerization conditions, (a) an addition polymerizable monomercontaining at least one degree of unsaturation, with (b) a metallocenecatalyst having two or more distinct and chemically different activesites, and (c) a catalyst activator, wherein the catalyst has thestructure B(Z)_(q) of structural formula (I) ##STR32## wherein: B is acovalent bridging group comprising carbyl, silyl, disilyl, germanyl,ammonium, phosphonium, ##STR33## or a C₁ -C₂₄ hydrocarbyl radicaloptionally containing a Group IVB element, a Group VB element, or both aGroup IVB element and a Group VB element, and is capable of binding upto n_(max) substituents through single covalent bonds, where n_(max) isat least 4;R and R¹ are independently selected from the group consistingof halogen, C₁ -C₂₄ hydrocarbyl, C₁ -C₂₄ hydrocarbyl substituted withone or more halogen atoms, and C₁ -C₂₄ hydrocarbyl-substituted Group IVBelements, x is 0, 1, 2, 3 or 4, and y is 0, 1, 2, 3 or 4, with theproviso that the sum of x and y cannot exceed 4, or, when R and R¹ areortho to each other and x and y are each 1 or greater, R and R¹ cantogether form a five- or six-membered cyclic structure optionallysubstituted with one to four substituents selected from the groupconsisting of halogen, C₁ -C₂₄ hydrocarbyl, C₁ -C₂₄ hydrocarbylsubstituted with one or more halogen atoms, and C₁ -C₂₄hydrocarbyl-substituted Group IVB elements; Q is J(R²)_(z-2) wherein Jis an element with a coordination number of three from Group VB or anelement with a coordination number of two from Group VIB, R² is selectedfrom the group consisting of hydrogen, C₁ -C₂₄ hydrocarbyl, C₁ -C₂₄hydrocarbyl substituted with one or more halogen atoms, and C₁ -C₂₄alkoxy, and z is the coordination number of J, and further wherein Qsubstituents on different Z groups may be linked through a C₁ -C₂₄hydrocarbylene bridge; M is a Group IIIA element, a Group IVA element, aGroup VA element, a lanthanide, or an actinide; X is selected from thegroup consisting of hydride, halide, alkoxy, amido, C₁ -C₂₄ hydrocarbyl,C₁ -C₂₄ hydrocarbyl radicals substituted with one or moreelectron-withdrawing groups, and C₁ -C₂₄ hydrocarbyl-substituted GroupIVB elements, or, when two or more X substituents are present, they maytogether form an alkylidene olefin, acetylene, or a five- orsix-membered cyclic hydrocarbyl group; Y is a neutral Lewis base; m is1, 2, 3 or 4, and n is 0, 1, 2 or 3, with the proviso that if M is aGroup IIIA element, m is 1 and n is 0, and with the further proviso thatif M is a Group IVA element, the sum of m and n does not exceed 2; ifn_(max) is 4 or 5, then q is 2, and if n_(max) is greater than 5, then qis an integer in the range of 2 to q_(max), wherein q_(max) is equal to1/2n_(max) when n_(max) is an even number, and 1/2 (n_(max) -1) whenn_(max) is an odd number; and at least two of the Z substituents boundto B are different.
 2. The method of claim 1, wherein the polymercomposition comprises a homopolymer.
 3. The method of claim 1, whereintwo or more different addition polymerizable monomers are used, and thepolymer composition comprises a copolymer.
 4. The method of claim 1,wherein the addition polymerizable monomer is an α-olefin having fromabout 2 to about 20 carbon atoms.
 5. The method of claim 4, wherein theα-olefin is a linear or branched olefin.
 6. The method of claim 5,wherein the α-olefin is selected from the group consisting of ethylene,propylene, 1-butene, 3-methyl-1-butene, 1,3-butadiene, 1-pentene,4-methyl-1-pentene, 1-hexene, 4-methyl-1-hexene, 1,4-hexadiene,1,5-hexadiene, 1-octene, 1,6-octadiene, 1-nonene, 1-decene,1,4-dodecadiene, 1-hexadecene, 1-octadecene, and mixtures thereof. 7.The method of claim 4, wherein the α-olefin is a cyclic olefin ordiolefin.
 8. The method of claim 7, wherein the α-olefin is selectedfrom the group consisting of cyclopentene, 3-vinylcyclohexene,norbornene, 5-vinyl-2-norbornene, 5-ethylidene-2-norbornene,dicyclopentadiene, 4-vinylbenzocyclobutane, tetracyclododecene,dimethano-octahydronaphthalene, 7-octenyl-9-borabicyclo-(3,3,1) nonane.9. The method of claim 1, wherein the addition polymerizable monomer isan aromatic monomer.
 10. The method of claim 9, wherein the aromaticmonomer is selected from the group consisting of styrene,o-methylstyrene, m-methylstyrene, p-methylstyrene, p-tert-butylstyrene,m-chlorostyrene, p-chlorostyrene, p-fluorostyrene, indene,4-vinylbiphenyl, acenaphthalene, vinylfluorene, vinylanthracene,vinylphenanthrene, vinylpyrene, vinylchrisene and mixtures thereof. 11.The method of claim 1, wherein the addition polymerizable monomer isselected from the group consisting of methylmethacrylate, ethylacrylate,vinyl silane, phenyl silane, trimethylallyl silane, acrylonitrile,maleimide, vinyl chloride, vinylidene chloride, tetrafluoroethylene,isobutylene, carbon monoxide, acrylic acid, 2-ethylhexylacrylate,methacrylonitrile, methacrylic acid, and mixtures thereof.
 12. Themethod of claim 1, wherein the catalyst is unsupported.
 13. The methodof claim 1, wherein the catalyst is supported.
 14. The method of claim1, wherein polymerization is conducted in the liquid phase.
 15. Themethod of claim 1, wherein polymerization is conducted in the gas phase.16. The method of claim 1, wherein polymerization is conducted in aslurry.
 17. The process of claim 1, wherein, in Formula (I), q is
 2. 18.The process of claim 1, wherein, in Formula (I), q is
 3. 19. The processof claim 1, wherein, in Formula (I):B is a covalent bridging groupcomprising carbyl, silyl, disilyl or a C₁ -C₁₂ hydrocarbyl radicaloptionally containing a Group IVB element, a Group VB element, or both;x is 0, 1 or 2; y is 0, 1 or 2; R and R¹ are independently selected fromthe group consisting of halogen and C₁ -C₁₂ alkyl, or are ortho to eachother and linked to form a cyclopentadienyl or indenyl group; J isnitrogen, phosphorus, oxygen or sulfur, and R² is C₁ -C₁₂ alkyl, C₁ -C₁₂alkyl substituted with a halogen atom, or monocyclic aryl; M is a GroupIVA element; m is 1 or 2, n is 0 or 1, and the sum of m and n is 2; X isselected from the group consisting of hydride, halide, amido, C₁ -C₁₂alkyl, C₁ -C₁₂ alkyl substituted with one or more halogen and/or alkoxygroups, and C₁ -C₁₂ hydrocarbyl-substituted Group IVB elements; Y is aselected from the group consisting of diethylether, tetrahydrofuran,dimethylaniline, aniline, trimethylphosphine, and n-butylamine; and q is2 or
 3. 20. The process of claim 19, wherein, in Formula (I), the Zsubstituents bound to B contain different M moieties.
 21. The process ofclaim 19, wherein, in Formula (I):B is carbyl, a C₁ -C₆ hydrocarbylradical or silyl; x and y are independently 0 or 1; R and R¹ areindependently selected from the group consisting of halogen and loweralkyl, or are ortho to each other and linked to form a cyclopentadienylring; Q is J(R²)_(z-2) wherein J is nitrogen, R² is lower alkyl orphenyl, and z is 3; M is Zr, Hf or Ti; m is 2; n is 0: X is selectedfrom the group consisting of hydride, amido, and lower alkyl; Y isdiethylether or tetrahydrofuran; and q is 2.